4 Frof. J. C. Poggcndorff on the Extra Current 



First by a bundle of iron wire. If such a bundle is inserted 

 in the accessory coil, tension and sparks are observed in the 

 junction wires to a surprising degree. The supposition is most 

 natural that this result arises from a strengthening of the opposite 

 current ; and if this supposition is confirmed, the inducing induc- 

 tion current must be enfeebled by the bundle of iron. This is in 

 fact the case. 



I was convinced of this in the following manner. I joined 

 an inductorium having 10,000 feet of wire to an accessory coil 

 of 23,000 feet, interposing at the same time a galvanometer and 

 a well-exhausted electrical egg — the latter for the double reason 

 of observing the luminous phenomena in it, and removing the 

 closing current, so that the hammer might be used ; for indi- 

 dividual openings and closings of the battery of six elements 

 had produced no result. 



By means of this arrangement, and without iron wire in the 

 accessory coil, I obtained a deflection of about 20° in the gal- 

 vanometer, and the well-known luminosity in the egg. When 

 the iron was interposed in the coil, the deflection sank at least 

 to half its amount, and the light in the egg disappeared almost 

 completely, being reduced to a few irregular sparks. 



Hence the strengthening of the opposite current, and there- 

 fore its existence, cannot be subject to any doubt. 



In what manner soft iron strengthens the opposite current 

 does not come into consideration. I will, however, remark that 

 an induction current magnetized the iron in the same direction as 

 that in which it deflects a magnetic needle, that it gives therefore 

 to Ampere's molecular currents the same direction as its own ; 

 while in an adjacent wire, according to the observations of Henry 

 and others, it produces an induction current of the second order in 

 an opposite direction*. By its magnetization the iron reacts on 

 the magnetizing induction wire, and as it produces in it an op- 

 posite current, I conclude that this current is the product of the 

 commencing magnetism, and the disappearing acts little, or not at 

 all. If in the momentary magnetization which the soft iron 

 experiences by the induction current, resulting from the opening 

 of the voltaic current, both elements, the increase and decrease 

 of the magnetism, were of equal influence upon that current, it 

 could not be perceptibly affected. 



A closed coil inserted in the accessory coil acts differently, 

 that is, enfeebles the opposite current, and therewith the tension ; 



* It is clear that an induction current, since in its transitory career it in- 

 creases and decreases, must induce two currents as well in its own as in an 

 adjacent wire, one of opposite and one of the same direction. But ac- 

 cording to all observations the first is, in galvanic induction, the stronger ; 

 hence I have only spoken of it, and called it opposite current. 



